Preparation, characterization and application of Nanaporous activated charcoal from plant resources
Date
2019
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Institute of Science and Technology, Chemistry
Abstract
This study was undertaken to prepare Activated Carbon (AC) from an agro-waste, i.e.
sawdust of Shorea robusta by chemical activation using phosphoric acid and
characterized and applied this AC in energy related field.
The carbonization of wood powder of Shorea robusta was carried out at 400°C in an
inert atmosphere of N
2
to prepare AC, which was chemically activated with H
vi
3
PO
4
and successfully tested as supercapacitor materials for the first time for its application
in energy storage device. Thermogravimetric Analysis (TGA)/Differential Scanning
Calorimetry (DSC), Scanning Electron Microscopy (SEM), X-ray diffractometer
(XRD), Raman spectra, Fourier Transform Infrared Spectroscopy (FTIR), Brunauer–
Emmett–Teller (BET), and X-ray Photoelectron Spectroscopy (XPS) are the methods
that have been utilized to characterize as prepared AC.
Thermal decomposition behavior (TG curve) coupled with endothermal peak of DSC
curve confirmed that 400
o
C was the adequate temperature for carbonization of raw
sawdust powder, since no significant weight loss occurred after 400
o
C, which
confirms the completion of carbonization process. FTIR spectra clearly confirmed the
presence of oxygenated functional groups such as hydroxyl (-OH), aldehyde/ketone (CHO/C=O)
and ether (C-O-C), at the surface of as prepared AC. Similarly, XPS
shows a broad peak at 532.6 eV for O 1s, indicating the presence of different
chemical states of oxygen and the three deconvoluted peaks for oxygen at the binding
energies 531 eV, 533.04 eV and 533.12 eV shows the presence of phosphatic oxygen
(PO
4
3-
), hydroxyl group (-OH) and silicon dioxide (SiO
2
) respectively. XPS spectra
confirmed that as prepared activated carbon (Sa-H
3
PO
4
) was well functionalized after
H
3
PO
4
activation and consists of more acidic functional groups as aldehydes/ketones,
ethers, hydroxides. This aligns with the FTIR results, where activated carbon (SaH
3
PO
4
) showed high intensities for hydroxyl (-OH), aldehyde/ketone (-CHO/C=O)
and ether (C-O-C) functional groups. XRD-pattern showed the amorphous structure
of carbon having 002 and 100 plane, whereas Raman spectra clearly displayed G and
D band which further confirms the amorphous nature of carbon. The G/D intensity
ratio was found to be approximately 1, which indicated the presence of graphitic
degree and defects in equal proportion. BET method of surface area determination
showed the high specific surface area of 1270 m
2
g
-1
(+ 0.57 %).
Electrochemical characterization was performed in 6M aqueous KOH using Cyclic
Voltammetry (CV), Galvanostatic Charge-Discharge (GCD) and Electrochemical
Impendance Spectroscopy (EIS). The specific capacitance acquired from GCD at 1 A
g
-1
was found to be 136.3 Fg
-1
(+ 0.15 %) with 0.44 Ω (+ 0.02 %) ESR. The 97 %
capacitance retention was observed after 1000 cycles. The energy density of as
prepared carbon electrode was found to be 3.0 (+ 0.25 %) Whkg
vii
-1
at 100.5 (+ 0.20 %)
Wkg
-1
power density. Then the working carbon electrode was replaced by hybridcomposite-electrode
which showed the ideal capacitive behaviors having specific
capacitance of 480.4 (+ 0.20 %) Fg
-1
, specific energy density of 24 (+ 0.26 %)
WhKg
-1
at power density of 149.3 WKg
-1
and low ESR value of 0.41 (+ 0.02 %) Ω.
The obtained results revealed that the desirable electrochemical capacitive
performances enable the hybrid composite to act as a new bio-material for high
performance supercapacitors and energy storage devices.
Keywords: hybrid composite, capacitive behavior, energy density, power density
Description
Keywords
Hybrid composite, Capacitive behavior, Energy density, Power density